By IANS, [RxPG] If you are a middle-aged man or woman and tend to over- exercise, then you may unwittingly damage your knees, increasing chances of osteoarthritis, a new study says.

'Our data suggest that people with higher physical activity levels may be at greater risk for developing knee abnormalities and, thus, at higher risk for developing osteoarthritis,' said Christoph Stehling.

Stehling is a research fellow in radiology and biomedical imaging at the University of California, San Francisco -.

Osteoarthritis is a degenerative joint disease that causes pain, swelling and stiffness. It affects 27 million adults in US, says the Center for Disease Control and Prevention.

The UCSF study involved 236 participants who had not reported previous knee pain and were enrolled in the National Institutes of Health Osteoarthritis Initiative.

The participants comprised 136 women and 100 men, aged between 45 and 55 years, within a healthy weight range.

They were categorised as low, middle, and high-activity groups based on their responses to the Physical Activity Scale for the Elderly - questionnaire.

PASE is a standard test that scores an older individual's physical activity level, based on the type of activity and the time spent doing it.

Several factors contribute to the final PASE score, but a person whose activity level is classified as high typically might engage in several hours of walking, sports or other types of exercise per week, as well as yard work and other household chores.